For reasons explained above in the cited document WO 01/88598, the apparatus further comprises means for imparting an exit divergence to the exiting light beams being transmitted through or reflected from the screen. The measure of the exit divergence substantially corresponds to the angle between neighbouring emitting directions associated with the optically neighbouring modules. The purpose of the exit divergence is to provide a substantially continuous motion parallax in the 3D image perceived by an observer, i. e. to ensure the substantially continuous change of a perceived 3D image.
The principle of generating a 3D image with the apparatus of the present invention is similar to that described in WO 01/88598, and the teaching of which is presumed to be known for the understanding of the present invention. However, a brief explanation is also provided below, with reference to FIGS. 1 to 7.
The apparatus is to provide three-dimensional images, i. e. images with a sense of space for the observer. A sense of space may be obtained if the observer perceives different views of an object when looking at the object from different directions. Accordingly, there is a need for an apparatus which is capable of emitting different light beams, depending on the angle into which they are emitted. This may be fulfilled by an apparatus having a working principle shown in FIGS. 1 and 2. This apparatus is indeed capable of emitting different light beams in different emitting directions, as explained in detail below with reference to FIG. 3.
For this purpose, the apparatus has a screen 20 that transmits and/or reflects light direction selectively. By the direction selectivity of the screen 20 it is meant that the exiting light beams Le exit the screen 20 depending on the incident angle of the projected light beam Ld arriving at the screen 20, i.e. a well defined emitting angle is associated to a given incident angle. In other words, the direction of the incident light beam Ld explicitly determines the direction of the exiting light beam Le, as opposed to diffuse screens, where after the incidence of a light beam other light beams exit in a relatively wide space angle and the direction of the incident exciting beam cannot be determined from a light beam exiting in a given direction.
There are screen points P in the screen 20, which are not necessarily physically distinguished, that is their position is determined by the incident and emergent light beams in a given case. It is also viable, however that the position of the screen points P is also physically fixed in the screen, for example 20 with appropriate apertures. In such cases the screen points P can also be physically separated by a borderline 21 between the screen points P, as illustrated in FIG. 3. In most cases, as in the examples described in FIGS. 1 to 6, the direction selectivity of the screen 20 is realised so that the screen 20 transmits the light beams Ld arriving at the screen points P without changing their directions, but other realizations are also possible. For example, the screen 20 may reflect the light beams Ld like a mirror or a retroreflector. Such embodiments are also described in WO 01/88598
The screen points P of the screen 20 can emit light beams of different intensity and/or colour in different directions. This feature of the screen 20 facilitates the operation of the apparatus as a three-dimensional display. FIGS. 1-3 demonstrate an embodiment, where light beams Ld practically do not change their direction when passing through the screen 20 and exit as light beams Le within the emitting angle range α.
The following annotation convention is used for the explanation of the contents of FIGS. 1 to 7, particularly FIG. 3. We assume that there are q number of modules in the apparatus, where we mark an arbitrary module with an intermediate index j from one of the 1 . . . q modules. A module can emit light beams in n different directions, the annotations for the arbitrary intermediate directions are i, m or g. There are p number of screen points P in the screen 20, the intermediate index is k. Light can emerge from a screen point P in n* emitting directions, this way n* emitting directions can be associated to a screen point P, and in this manner also to the whole screen 20. The intermediate indexes used here are i*, m* or g*. In the case of light beams, the lower index (s, c, d, e) refers to the function of the light beam in the optical system, where Ls represent light beams emitted by the light source, Lc represent collimated light beams, Ld represent deflected light beams, and Le represent the light beams finally emitted from the screen 20 towards the observer. The upper indexes refer to the module in line, the emitting direction related to the module and the concerned screen point P of the screen. Therefore, a light beam Lej,g,k+1 indicates that the light beam exits from the screen 20, emitted in direction g from module j, touching (in this case emerging from) the k+1-th screen point P.
The light beams are generated by an illumination system within the apparatus. This system contains modules for generating the deflected light beams Ld and, indirectly, the emitted light beams Le. The light beams Le are associated to multiple different points of the screen 20, and they are also associated to different emitting directions E of the screen points P. For example, in the embodiment in FIG. 3, a module 45 contains the light source 70, and the light beams Ld1-Ldn emitted by the j-th module 45j pass through the different screen points Pk−2, . . . , Pk+2 of the screen 20. It is also visible that as a continuation of every deflected light beam Ld1-Ldn, the emitted light beams Lej,l,k−2, Lej,i,k−1, Lej,m,k, ej,g,k+1, Lej,n,k+2 exit from the screen 20, propagating in different E1-En, emitting directions. At the same time, light reaches the same screen point P from other modules. See for example in FIG. 3 that the light beam Ld1 emerging from the j−1-th module 45j−1 also reaches screen point Pk+1, and emerges in a different direction E than light beam Ldg coming from of the j-th module 45j. The light sources 70 may be realised with a single bulb 80, the light of which is distributed to the light sources through light guides 75 with a common end 76. The modules 45 may contain appropriate collimating optics 60 and focussing optics 40.
The individual modules are controlled by an appropriate controlling system according to the principles explained below. The function of the 45 modules is to project light to the screen points P of the screen 20 in different emitting directions within the emitting angle range α, with appropriate intensity and/or colour from the given screen point P towards the different emitting directions, realising a light source S emitting light in an angle range β (see FIGS. 1 and 2). This angle range β essentially corresponds to the emission angle range α of the screen 20. As seen in FIG. 1, light source S1, S2, S3, . . . , Sn emits an light beam Ld to screen point P3 and the direction of the light beams Le emerging from screen point P3 will be determined by the mutual position of the individual light sources S1-Sn and screen point P3.
The apparatus described in WO 01/88598 intended to provide an optical arrangement that could simulate light sources S, having an ideally zero width, in order to generate deflected light beams Ld that could be precisely directed towards a screen point P, the latter also having an ideally zero width.
The light beams Le creating the views associated to the different E1-En*, emitting directions from the individual screen points P and associated to several different screen points P of the screen 20 of the inventive apparatus are generated with the apparatus described in WO 01/88598 the following way: There are two-dimensional displays, namely 50 microdisplays in the individual modules 45. A lens images simultaneously the pixels Cd of an image to the screen 20. The image is displayed by the display 50. In the two-dimensional display 50, the pixels Cd are associated to the different screen points P and they are also associated to the different emitting directions E1-En* of the screen 20. The individual emitting directions E are actually determined by the deflection directions D of the light beams Ld emerging from the module 45.
The optical system projects the display 50 with the light beams Lc to an optical lens 40. The light beams Lc are modulated by the information encoded in the pixels Cd of a composite image, where this composite image is produced by the display 50. Thus, the light beams Ld are modulated by the information coded with the individual pixels (i.e. by the information carried by the pixels) of the image generated by the displays 50. The modules 45 are positioned periodically shifted, in optically equal or optically symmetrical positions in relation to each other and the screen 20.
It is perceivable that the optical lens 40 deflects the incident, substantially collimated, light beams Lc with a given angle, depending on the co-ordinates of the incidence. For example, as illustrated in FIG. 3, the light beam Lc1 passing through the pixel Cdj,1 at the left edge of the 50j SLM will be deflected to a deflection direction D1 which is different from the deflection direction Dm of the light beam Lcm passing through the pixel Cdj,m in the middle part of the 50j SLM. The light beam Ldm passes through the screen 20 in the Em emitting direction, in accordance with the fact that the Em emitting direction is determined by the Dm deflection direction. It is also clear from FIG. 3 (see also FIGS. 1 and 2), that, because of the different deflection directions, the light beams Ld deflected to different deflection directions D1-Dn by the common 40j optical lens pass through different screen points P.
Within the emitting angle range α, determined by the emitting directions E, light is emitted in practically all directions. Therefore, when viewing the screen 20 from this region, light beams reach the observer's eye from all screen points P (see also FIG. 5). Thus the emitting angle range α is practically identical with the complete viewing angle region, i.e. with the angle region within which the light beams from screen points P reach the eyes of the observer looking at the screen 20, or more simply, this is the region from where the observer is able to perceive some sort of image on the screen 20.
The principles of the 3D imaging are explained in more detail in the following:
In the emitting angle range α the individual light beams Lc propagate in well determined emitting directions E. Viewing the screen 20 from a direction opposite these emitting directions E, light beams leaving the individual screen points P may be seen, and therefore a complete image is perceived on the whole of the screen 20, this complete image being composed of the screen points P. It must be noted that in the image appearing for the observer the surface of the screen 20 and the screen points P themselves may not necessarily be perceived, and the image perceived will not be seen by the observer as a two dimensional projection of view, but the observer will experience the feeling of real space.
It is demonstrated in FIG. 4 that there may be a great number of modules 45 behind the screen 20. With the divergence of the screen 20, it is ensured that a light beam arrives to the eyes of the observer from all directions from each screen points P, which allows the observer to perceive a continuous image within the angular region. As it is shown separately on the right hand side of the FIG. 4, the light beams Leg−1, Leg−1, Leg+1—which reach the screen 20 as collimated non-divergent beams—leave the screen point P in different directions. These beams are dispersed by the screen 20 with the angle δx, making them slightly divergent. The same effect is shown in detail in FIG. 5. This way light reaches the eyes E2L of the observer, even though the direction of both light beams Leg−1, Leg had originally missed the observer's eyes. It may be noted in FIG. 4 that the light beam Leδg reaching the observer's eyes E2L seems to be the continuation of the virtual light beam Leδg′, which itself seem to start from between two modules 45 and pass through the screen point P. This way there is no “gap” between the light beams Leg−1, Leg, Leg+1, the visually perceived image is not flawed with unlit parts, and the viewing region is continuously covered, i.e. a continuous motion parallax is achieved.
This divergence of the emitted light beams Le was achieved by a diffuser screen in the apparatus disclosed in WO 01/88598. The present invention proposes a method and an apparatus to improve the quality of the 3D image, with or without the use of such a diffuser screen.
It is also clearly seen that the complete view associated to the individual viewing directions is not produced by one module, but by several modules, see particularly left side of FIG. 4. This image arrangement ensures that if the observer changes position, and his viewing point changes, for example, by moving in the direction of the arrow F, the light beams Lcg−1, Leg1, Leg+1 and the perceived light beams Ldg−1, Ldg, Ldg+1 emitted by the modules 45 also change continuously, creating the image perceived by the E2L eye, the position of which is continuously changing (see right side of FIG. 4). In this manner, a continuously changing image is created, in accordance with the fact that the Ldg−1, Ldg, Ldg+1 light beams are created by different modules 45 (see FIG. 4). It is also clearly shown that beams from different modules 45 reach the right eye ER and the left eye EL of the observer from the individual screen points Pk−1, Pk, Pk+1, Pk+2 etc. This basically means that the same screen point is able to transmit different information for the left and right eye.
The same effect is represented in an even more detailed fashion in FIG. 5. In this figure we present how the apparatus according to the invention displays the spatial points of different three dimensional objects. As an example, in FIG. 5, the apparatus displays two dark point objects O1 and O2 and two light point objects O3 and O4, which are perceived as being suspended in a three dimensional space for two observers in two different positions. For better understanding we primarily indicated those light beams of the modules 45 which actually reached the eyes of the observers, but it must be emphasised that there are light beams leaving all modules in all emitting directions. Therefore, the apparatus is independent of the position of the observers and provides a real 3D image when viewed from any direction within the field of view, without the use of special glasses or any other hardware worn by the observers. In FIG. 5, for example, it is shown that, the first observer will perceive the dark object O1 with both eyes E1R and E1L, but to achieve this the module 45i−8 transmits a light beam to the right eye E1R, while the light beam to left eye E1L is transmitted by the module 45i. This way the observer will clearly perceive that the light from the object reaches his two eyes from different angles, and he/she will also perceive the distance from the object O1. Not only does the first observer perceive the object O2 as well, but he/she can also sense that for him/her the object O2 is behind the object O1, because the observer only receives information about the object O2 through his/her E1L left eye, through the light transmitted by the module 45i−2 in the direction of the left eye E1L. At the same time, for the second observer the objects O1 and O2 will appear as two distinct objects, according to the light beams reaching his/her, eyes E2R and E2L from the modules 45i+17 and 45i16, and the module 45i+8. The left eye E2L of the second observer cannot see the object O1, because the light beams arriving from its direction cannot be produced by any of the modules. On the other hand, on the basis of the same principles, both observers will see the point objects O3 and O4. For example, the light object O4 will be perceived by both eyes of the first observer on the basis of the light exiting the modules 45i+3 and 45i, and the modules 45i−8 and 45i−11. It is noted that owing to light beams, which may be emitted in different directions and with different intensity, the same module 45i, for example, is able to display a different colour object for the first observer's right eye E1R and left eye E1L. The right eye E2R of the second observer does not perceive the object O4, because it is obstructed by the object O2. The second observer can only see the object O4 with his/her left eye E2L. It is obvious that the apparatus is capable of displaying any number of point objects of this sort, and this way it is also suitable for displaying objects of finite dimensions, since these objects may all be displayed as sets of points. We can also see that objects in front of and behind the screen 20 can equally be displayed with the help of the apparatus. The light beams produced by the apparatus are exactly the same as if they had started from the object to be displayed, and the projecting arrangement does not take into consideration the position of the observer. A lifelike image is displayed in all directions within the emitting angle range, regardless of the position of the observer. It is emphasised here again that the apparatus continuously emits light beams in directions where there are no viewers at all. Such light beams are represented in FIG. 5 as light beams Le.
As mentioned above, the perception of 3D objects with good visual quality requires that the exiting light beams Le have a certain divergence when they leave the screen 20. For example, this may be achieved by applying a holographic diffusing screen. The diffusive property of the screen 20 ensures that the substantially collimated output beams will leave the screen points P with a divergence δx, with a maximum of few degrees, so that there is an overlap between the light beams Ldi, Ldi+1 arriving from the modules 45. In the case shown in FIG. 7A, the directions of the deflected light beams Ldi, Ldi+1 are practically the same as the directions of the emitted light beams Lei, Lei+1, and these also represent adjacent emitting directions. Apparently, the overlap, i.e. the tight contact of the adjacent light beams Lei, Lei+1 is appropriate, when the divergence angle δx is the same as the angle γ between the emitted light beams.
However, there is a problem with the approach where the necessary divergence δx of the emitted light beams Le is achieved with a diffusive screen, as shown for a single module 45 and a single deflected light beam Ld in FIG. 6A. In this case, the intensity distribution of the emitted light beams Le is similar to the angular intensity distribution shown in FIG. 6C, namely it is largely Gaussian, with a strong central region and lowering intensity towards the edges. As a result, the combined intensity distribution of several neighbouring emitted light beams Le will follow the curve in FIG. 7C. Depending on the angle of divergence δx disturbing side effects are present in the image. In case the angle of divergence δx is small the observer will perceive a fluctuation of the intensity, i.e. inhomogenities will appear in the image. In case the angle of divergence δx is sufficient to compensate intensity inhomogenities, the observer will perceive visual noise caused by the crosstalk in the region 5 where the neighbouring light beams overlap. For the observer, it means that the perceived image will be blurred, the neighboring views will be simultaneously present in the three dimensional image and the apparatus is not capable of showing images with sharp contours.
The screen diffusion characteristic is a critical factor in such systems, and unfortunately, this Gaussian intensity distribution is inherent in all practical diffusers even in holographic diffusion screens. The uneven total intensity shown in FIG. 7C or the undesirable crosstalk is practically unavoidable since these are conflicting requirements. This strongly limits the performance of such systems and makes manufacturing high quality 3D displays impossible. This is true for systems with achromatic holographic diffusion screens or if not holographic screens are used but other dispersing components, for example a lenticular lens system, it is difficult to realise the ideal diffusion characteristic (see FIGS. 6B, 7B) and serious alignment, colour dispersion problems arise, which again cause a deterioration of the perceived image.